The town's name derives the presence of the river Nahar (Black). It is a municipality in the province of Terni, located on a rocky outcrop, whose location and views open over the Black River Gorge and on the plain of Terni. The town, with its fortified houses, still surrounded by ancient walls, is dominated by the imposing bulk of the XIV century fortress, that seems to watch out over vast surrounding areas. Lower in the valley, the new town has recently developed and borders with the industrial area of Terni.
An ancient Umbrian settlement, that around 299 B.C. became a Roman colony. Originally just a coach station along the Via Flaminia, it was later proclaimed Municipium. After the fall of the Roman Empire, the area was prey to the barbarian invaders, and was occupied by the Lombards, that incorporated the territories into those of the Duchy of Spoleto, which later became part of the papal possessions. In medieval times, the town supported the Guelphs, that overcome the Papal domain, so in the XIV century, the Cardinal Albornoz was obliged to resume the control of Narni with the force. In the first half of the XVI century the main center was seriously damaged by the troops of Charles V, but later rebuilt thanks to the efforts of the Papal States and to whom it belonged until its annexation to the Kingdom of Italy.
- the Cathedral, dedicated to St. Juvenal, which was built in XII century in Romanesque style, is also the tomb of the Saint. The building was enlarged in the XIV century, while embellished at a later date with a portico. The interior is divided into four aisles, the last one was added in the XV century, and ends with a polygonal apse with Gothic frescoed arches;
- the church of Santa Maria in Pensole, built in 1100, features a façade preceded by a porch with beautiful portals. The interior features three naves and a series of XIV century frescoes;
- the Church of San Francesco, which was built in the XIV century in Gothic style. Within it features three naves decorated with frescoes from the XIV and XV centuries;
- the Oratory of St Juvenal in Gassio, which preserves a series of valuable paintings, sculptures and frescoes and the tombs of Cesi and of the Bishop Gormaz;
- the XII century Church of San Domenico, which preserves an important collection of sculptures and frescoes;
- the Church of St. Augustine, of the XV century, rich in artworks;
- the Bridge of Augustus, named so because its building dates back to period of Augustus. Of the original four-arched structure remains only one;
- the Palazzo del Podestà, built in the XIII century, features three tower-houses incorporated into one unique complex. The façade features precious Romanesque carvings of the XIII century and today the building houses the Art Gallery;
- the XIV century Fortress, built by Cardinal Albornoz, features a square plan building with corner towers and a keep;
- the XIV century Palazzo dei Priori, which is famous for its loggia and its pulpit;
- the Civic Tower.